We have had this problem with a few of our providers. When they originally signed up for Medicare they did under their ss#. Then somewhere along the line they started using a Tax ID#.
This may not work for you but for one of my providers in particular I am submitting the claims under her ss# while we are waiting for the paperwork to be processed. This is not an ideal situation, but it is necessary for her. Since she is a PC under her tax ID# Medicare is considering her non par from May 23rd until the date she signed a new participating provider agreement. However, under her ss# she is par so we are submitting claims that way. Any claims that are crossed over to the secondaries may get sent over under her ss# though and then the 2ndary may not recognize her. We will just have to fix those as they arise. It is better than the other option.
I do know of others who also sent in under the ss# during the wait. I can't guarantee it will work for you, but you may want to look into it.
Good luck
Michele